1. Field of the Invention
The present invention relates to a method of fabricating an organic electroluminescent display(hereinafter abbreviated OELD) enabling to improve device characteristics and reliability by performing excimer laser annealing on a passivation layer without affecting any other elements of the device.
2. Background of the Related Art
As information communication technology is greatly developed, demands for electronic displaying means are highly increased in accordance with a variety of information societies. So does the demand for various displays. In order to meet the demands of the information society, for electronic display devices are required characteristics such as high-resolution, large-size, low-cost, high-performance, slim-dimension, and small-size and the like, for which new flat panel display(FPD) is developed as a substitution for the conventional cathode ray tube(CRT).
In the presently developed or used flat panel displays, there are Liquid Crystal Display(LCD), Light Emitting Display(LED), Plasma Display Panel(PDP), Vacuum Fluorescence Display(VFD), Electroluminescent Display(ELD) and the like.
Compared to the non-emissive device, ELD (electroluminescent display) attracts attention as a flat panel display having characteristics such as a response time faster than that of the non-emissive device such as LCD, an excellent brightness due to self-emission, an easy fabrication from a simple structure, and a light weight/slim design. ELD is applied to a new flat panel display (FPD) as a next-generation substitute. ELD is generally divided into two categories, i.e. an organic electroluminescent display (hereinafter abbreviated OELD) and an inorganic electroluminescent display (hereinafter abbreviated IELD) in accordance with materials used for luminescent layers.
In the above-mentioned OELD, a conductive transparent anode layer, a hole injection layer, a hole transport layer, an organic electroluminescent layer, an electron transport layer, and a cathode layer are stacked successively on a transparent substrate formed of glass, quartz or the like. In this case, an organic material constructing the organic electroluminescent layer is very sensitive to oxidation, moisture, and contamination due to impurities, thereby needing an airtight passivation layer. Specifically, the cathode layer is formed of a metal having a low work function in order to reduce a driving voltage and achieve efficient electron injection. Such a metal is very sensitive to external oxygen and moisture. Namely, the oxidation of the metal constructing the cathode layer degrades luminescent characteristics of the device such as luminescent brightness, uniformity of luminescence and the like badly, thereby reducing the life-time of OELD.
Moreover, when defects such as pinholes and the like exist in a metal surface of the cathode layer, oxygen, moisture and the like penetrate into the organic electroluminescent layer through these pinholes so as to degrade the organic electroluminescent layer. Therefore, the device characteristics are abruptly degraded. In order to secure the reliability of QELD, the organic electroluminescent layer as well as the pinholes in the cathode layer should be cut off from an ambient atmosphere so as to prevent the degradation.
One of the methods for shielding the organic electroluminescent layer of OELD from an external environment is using a metal cap.
FIG. 1 illustrates a cross-sectional view of an OELD using a metal cap according to a related art.
Referring to FIG. 1, an OELD 10 using a metal cap 20 is fabricated in a manner that an anode layer 12 formed of a conductive transparent material is stacked on a transparent substrate 11. And, on the anode layer 12 successively stacked are a hole injection layer 13, a hole transport layer 14, an organic electroluminescent layer 15, an electron transport layer 17, and a cathode layer 18. The anode, hole injection, hole transport, organic electroluminescent, electron transport, and cathode layers 12, 13, 14, 15, 17, and 18 stacked on the transparent substrate 11 are sealed using a metal cap 20 having a desiccant 19 at a center inside and a sealant 21.
In the OELD 10 having the above-constructed metal cap 20, when a voltage is applied between the anode layer 12 and the cathode layer 18, holes move from the anode layer 12 into the organic electroluminescent layer 15 through the hole injection layer 13 and hole transport layer 14 while electrons move from the cathode layer 18 into the organic electroluminescent layer 15 through the electron transport layer 17. Thus, the organic electroluminescent layer 15, where the injected holes are combined with the injected electrons to generate the emission of light, emits lights. In this case, the hole injection, hole transport, and electron transport layers 13, 14, and 17 play an auxiliary role in increasing an efficient luminescence of OELD.
Unfortunately, the metal cap having the desiccant is left apart from a surface of the cathode layer in the related art. When the metal cap fails to secure 100% sealing by the sealant, the organic electroluminescent and cathode layers become contacted with oxygen and moisture so as to cause the degradation. Thus, it is difficult to protect the device completely only with the desiccant existing in part. Moreover, steps of attaching the desiccant and metal cap to the CELD are very complicated.
Accordingly, the present invention is directed to a method of fabricating an organic electroluminescent display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of fabricating an organic electroluminescent display(hereinafter abbreviated OELD) enabling to improve device characteristics and reliability by preventing organic electroluminescent and cathode layers from being contacted with oxygen, moisture and the like.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, a method of fabricating an organic electroluminescent display according to the present invention includes the steps of forming an anode layer, an organic electroluminescent layer, and a cathode layer successively on a transparent substrate, forming a passivation layer on the transparent substrate including the cathode layer, and performing local heat treatment on the passivation layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.